The present invention relates to a radiant beam coordinate detection system, more particularly, to a crossed infrared beam coordinate detection system.
Crossed infrared beam X-Y coordinate detection and encoder systems are well known in the art. See U.S. Pat. Nos. 3,764,813; 3,775,560; 3,860,754; 4,243,879; 4,267,443; and 4,384,201, for example. Typically in these systems x and y coordinate arrays of paired infrared light sources and detectors are caused to scan a display surface with crossed light beams by an electronic scanning system. When any of the beams are interrupted the prior art detection systems are equipped for determining the position of the interrupted beams.
Problems encountered in the design of a crossed radiant beam coordinate detection system such as those described above include: ambient light interference which produces radiation in the IR spectrum that can interfere with operation of the system; wide variation in performance of optoelectronic devices due to differences in optical and mechanical axes; aging of emitters which reduces their output; scattering, reflection, and attenuation effects due to the housing used for mounting the emitter/detection pairs; and the optical alignment of emitters/detectors.
U.S. Pat. Nos. 3,764,813, 3,775,560 and 3,860,754 disclose systems in which the arrays of emitters and detectors are electronically sequentially scanned. This helps reduce problems due to emitters/detectors being non-aligned and the effects of scattering, reflections etc.
U.S. Pat. No. 4,243,879 discloses a means for compensating for a light fluctuations in the performance of crossed beam coordinate detection and encoding systems, while U.S. Pat. No. 4,267,443 and 4,384,201 disclose among other things a means for determining the relative size or center line of the object which is interrupting the beams.
Despite the advantages of the above described systems a need still exists for an improved crossed beam coordinate detection and encoding system which addresses the above problems with greater flexibility.